I. Field of the Invention
The present invention relates generally to ceramic cutting tools and, more particularly, to a ceramic cutting tool especially suited for cutting ferrous metals, especially cast iron.
II. Description of the Prior Art
Ceramic cutting tools have been previously used for a number of different machining operations for machining metals. Such machine operations include shaping, milling, planing, turning, drilling and the like. In each instance, however, there is relative movement between the cutting tool and the workpiece in order to perform the machining operation.
In certain applications, ceramic cutting tools enjoy distinctive advantages over other types of cutting tools, such as high speed steel and tungsten carbide tools. In particular, ceramic cutting tools are typically used in high speed cutting applications.
Ceramic materials, most notably alpha alumina (Al.sub.2 O.sub.3) have been used to produce cutting tools which are capable of operation at higher speeds than the previously known steel and tungsten carbide cutting tools. The tool life of these previously known ceramic cutting tools, however, is often less than the previously known tungsten carbide cutting tools because the ceramic cutting tools are more brittle and less tough than carbides. Furthermore, the impact tolerance of the previously known ceramic cutting tools is relatively low so that such tools are operated at low tool feed rates. Consequently, the actual rate of metal removal is comparable to tungsten carbide tools even though ceramic tools are employed at higher cutting speeds.
There have been a number of different types of compositions used for ceramic cutting tools which are designed to increase the fracture toughness and life of the cutting tool For example, U.S. Pat. No 4,789,277 to Rhodes et al. discloses a cutting tool which is reinforced with silicon carbide whiskers in order to increase fracture toughness. Numerous commercial cutting tools are known which mix titanium carbide to the aluminum oxide in order to enhance the cutting characteristics of the cutting tool.
All of these previously known cutting tools enjoy certain advantages in certain machining operations and suffer certain disadvantages in other machining operations. For example, certain types of ceramic compositions have been found to be particularly useful for machining certain types of metals and yet ineffective for machining other types of metals. Similarly, the addition of certain materials, such as silicon carbide whiskers, significantly increases the overall cost of the ceramic cutting tool and, for that reason, is disadvantageous.
While the previously known ceramic cutting tools have proven effective in cutting ferrous materials, such as cast iron, such ceramic materials have exhibited a short, and therefore undesirable, tool life. While the addition of some materials, such as silicon carbide whiskers, increases the tool life when cutting ferrous materials, the addition of such materials also significantly increases the cost of the ceramic cutting tool.